Phase modulation transmitter



' Dec. 19, 1939. 2,183,905

M. L. DULL PHASE MODULATION TRANSMITTER Filed Marchl, 1953 3 Sheets-Sheet 1 95 MICRO AMPLIFIER Dec. 19, 1939. M, BULL 2,183,905

PHASE MODULATION TRANSMITTER Fil'ed March 1, 1933 3 Sheets-Sheet 2 19, 1939. M. DULL PHASE MODULATION TRANSMITTER 3 Sheets- Sheet 3 Filed March 1, 1955 Snot/nu m Patented Dec. 19, 1939 UNITED STATES ATENT FFiCE PHASE MODULATION TRANSllflTTER Application March 1, 1933, Serial No. 659,231

3 Claims.

This invention relates to intelligence transmission and reception, and more particularly has reference to a phase modulation system and transmitter in accordance with factors desired to be transmitted and received or utilized at some distant point.

As will appear more fully, the present system has an extremely wide field of use. However,

, since the fundamental principles of the concept can well be explained by an embodiment in radio transmission and reception, and since this field includes the essentials of facsimile transmission and remote control, this particular embodiment will be chosen for illustration.

A major object of the present invention therefore is to overcome the disadvantages of amplitude modulation.

Another object is to provide a novel system of modulation.

Another object is to devise a system of modulation which increases the utility of the radio broadcasting spectrum.

A further object is to provide a novel system of radio transmission and reception.

Yet another object is to provide a new system of transmitting and receiving intelligence utilizing electro-magnetic waves as the carrier or transmitting medium.

Yet another object is to provide a novel method of remote actuation or control.

In order to more clearly explain the principles of the invention, a physical embodiment in a radio transmitting and receiving system is shown in the accompanying drawings, of which:

Fig. l is a circuit diagram of one type of transmitter.

Fig, 2 is a modification of the circuit shown in Fig. 1.

Fig. 3 is a further modification of a transmitter made in accordance with the present invention.

Fig. 4 is an electrical diagram of a receiver.

Fig. 5 is a schematic representation of the units comprising the complete radio system.

Fig. 6 is a graphic illustration of the type of modulation which represents prior practice.

Figs. 7 and 8 are graphic illustrations of the essential operation of the present system.

Phase displacements are utilized in the present system to effect modulation. In Fig. 8 is shown the eiTec-t of capacitance in dot-dash line, and of inductance in dotted line. It will immediately be appreciated that in the new system the modulating effects are impressed directly on the transmitting vehicle, in radio the carrier wave, and in a mechanical analogy may take the form of a lateral displacement of one of the phase com-' ponents. This sharply differentiates from the prior art method where the modulating effects in wave form are, in a sense, superimposed on the carrier and anew resultant wave form of accenl tuated differential amplitude obtained. Thus with the older method the so-called modulated carrier is not in efiect a carrier but a new wave or, at the least, a markedly modified carrier. With the new system the so termed carrier is in truth a carrier, for it retains its identity of frequency and amplitude even after the modulation effects have been impressed. The present system then presents all the advantages of transmission on a carrier of substantially fixed or constantv amplitude and the obvious advantages of a receiving system designed to be responsive to a transmitted Wave of varying phase.

The essential diiferences between amplitude type of modulation and the new system of phase relationship may be more readily comprehended by a study of the mechanical analogy depicted in Fig. 7. Whereas in the amplitude modulation system, as shown in Fig. 6, the modulation frequency may be considered as superimposed on the carrier to give a new resultant wave form-- the operation of the new system may be considered as comprising a helix. During modulation the dimensions of the helix remain unaltered and the modulating efiects are caused by a shift or reciprocation of a factor up to ninety degrees on each side of a center point on half a turn. If the helix is now considered as a sign wave, it will be seen that the efiective modulation may be construed, as a shifting of the modulating factor to a predetermined degree on opposite sides of the half wave. In other words, the modulating factor may be considered as a linear reciprocation or oscillation on a curvilinear locus, where the curvilinear locus is the energy wave form and the oscillating or reciprocating factor is one of the phase components.

As will be explained more fully, a number of the components of the phase of the carrier energy may be utilized to efiect modulation. In order to clearly explain the system a preferred modification involving the utilization of voltage phase angle will be described.

In the operation of the improved system the equivalent of one hundred percent modulation is represented by a condition in which the voltage phase angle of the carrier, at thetransmitter, is caused to lead by a varying degree up to 90 the unmodulated angle for one peak half wave of the modulating frequency, and then to lag to the same degree the other half of the unmodulated phase angle for the opposite peak half wave.

For receiving the specially modulated carrier, the incoming energy is mixed with an alternating current energy having the same frequency and strength as that used. in transmission but differing from the latter in having a mean or constant voltage phase angle. This latter or local oscillation is unmodulated. The conditions are so controlled that the reaction between the transmitted energy, having a variable voltage phase angle, and the local energy of a mean or intermediate voltage phase angle, produces the exact form and character of the modulation energy used at the transmitter. At this point it will be appreciated that since thermionic tubes are voltage operated devices, they are immediately available in carrying out this system of modulation.

The receiver may be provided, as the exigencies of the particular case demand or require, with any desired number of amplification stages and the energy of the reception unit may be utilized either directly or may be transmuted into any other desired form or type of energy to operate mechanical, electrical or hydraulic control. Manifestly such control may be made either optional or automatic.

The transmitting circuit, as shown in Fig. 1, comprises essentially a stage IE3 for generating radio frequency oscillations (or the other oscillations utilized as a carrier), the isolating stage H and the effective phase control stage l2. The phase control stage 12 is associated with a stage 53 through which the intelligence is made to act on the phase control stage.

The output is coupled to a radiator, such as the antenna circuit M.

The isolation stage H and the phase control stage l2 are shown as comprising in effect dual units. These are thus designed because of these stages performing a dual function.

The isolating stage II serves to segregate the generator stage Ii) from the control stage l2 and functions to prevent undesired reactions of the phase control circuit on the generator circuit, such for example as changing or varying the load taken from the generator stage and fed through the system. This circuit or stage it additionally functicns to prevent undesired reactions within the phase control circuit it, such as would occur if the input grids of the tubes in stage H! were common to one circuit.

Similarly the phase control circuit l2 subserves a dual function. In the first place, it modifies the phase characteristics of the alternating energy from the output of the generator stage, in accordance with the input energy from the intelligence source l3. In the second place it serves to pass on the frequencies from the generator stage with unvarying output amplitude and frequency.

It will be seen from an inspection of Fig. 1 that the tubes comprehended within the different stages are fed from a power supply 54.

The power supply may comprise a power line l5 connected to transformer H at primary it. This Winding has a voltage adjusting tap 23. The core of the transformer is grounded at Hi. The transformer is provided with a plurality of secondaries is, 29, 2| and 22. Secondary l9 supplies high voltage to the rectifying and filament system, consisting of rectifying tubes 35 and 23; and filament heating winding 26; tap 20 and lead 2%. Tap 24 of secondary I9 is the negative terminal connecting to voltage dividing resistor 2?. Tap 20 of secondary 29 is the positive terminal connecting to lead 28. Secondary 251, as above noted, supplies heater current to the rectifying tubes. secondaries 2| and 22 supply heater current to the tubes in the radio fre-'- quency portion of the transmitter.

In the preferred modification, at some point near midway the voltage divider-resistor 21 is connected to the common ground 29 and to the intermediate filter condensers 30. It will be seen that since the cathodes of the tubes in the transmitter proper are at common ground potential,

points between the ground point of the voltage divider and the positive end may be used to give varying degrees of positive potential. Similarly from the same grounded cathode condition, points between the grounded point of the voltage divider and the negative end may be used to give varying degrees of negative potential.

It is to be clearly understood that since modulation is here secured by a control of the phase characteristics, the radio frequency generated by the oscillator is entireiy a point of reference in the radio system to which the transmitter will operate. The radio frequency generator may comprise a thermionic tube 3! and is preferably of the indirectly heated cathode, screen grid type. This is provided with a cathode and a heating element for the cathode.

As shown, the cathode or electron emitting element is connected to the common ground through the potentiometer resistance 32. The moving arm of the potentiometer, by-passed to the common ground by condenser 33, is connected to the control grid of the tube. The purpose of this arrangement is to establish an independent and variable source of grid bias so that the electronic flow to the screen and hence the screen and plate current drawn by the tube may be controlled.

In the tube shown in the illustration the screen carries a higher potential value than the plate and is thus operated on the dynatron or secondary emission principle. The frequency of oscillation of the tube is governed by the resonant period of the oscillating circuit connected to the plate and comprises the inductance 34 and variable condenser 35. The low side of this circuit, as well as that of the screen, is bypassed to the common ground by the condensers 38 and El and is additionally filtered by choke coils 38 and 39. The output of the oscillator is taken off from the high side of the plate circuit by the variable condenser M3. The utilization of a variable condenser at this point allows for a variation of the excitation to the subsequent tubes in the system.

The output of the oscillation generator stage iii is connected through the variable condenser 40 to the isolating circuit II. It will be noted at this point that this circuit branches out in the form of a V. This is advisable since from this point on to the antenna the circuit is in dual form. This dual form has been found at the present time best suited to perform the dual function incident to the isolation circuit 5 l and the phase control circuit i2. The output of the oscillation generator is therefore connected through the variable con-denser it! and leads 4| and 62 respectively to the control grids of thermionic tubes i3 and M. These tubes, similarly to the tube employed in the first stage, are of the indirectly heated cathode screen grid type, although manifestly other specific types may be employed.

also insures the proper functioning of the units in the phase control circuit.

The cathodes of the tubes in stage II are directly connected to the common ground as shown. The control grids, as noted, are connected to the center point of the Y connection. This center point is also connected with the aperiodic choke coil '34. This choke coil allows the control grids to follow the excitation of the frequency source I!) and at the same time to be under the stabilizing control of a constant value of negative potential. The low end of the choke coil M is bypassed to ground by the condenser Q5.

This low end is also connected, as previously described, to the correct degree of negative potential at the power supply, through the lead 46.

The screens of tubes 43 and M are bypassed to ground by condensers 4'! and 48 respectively and are additionally filtered by choke coils 49 and 5B. The low end of these choke coils go to a common connection, lead 5 I, and through this are supplied with the proper degree of positive potential from the power supply.

The plate of tube 43 is connected to the C/L circuit includingthe inductance 52 and the capacity 53. Similarly the plate of tube 44 is connected to the C/L circuit, including the inductance 54 and variable capacity 55. The low end of circuit 52-53 is bypassed to the common ground by condenser 56 and is additionally filtered by choke coil 51. The low end of choke coil 51 is connected-by lead 58 to the correct degree of positive potential in the power pack. Similarly circuit54-55 is bypassed, through condenser 58, to the common ground and is additionally filtered by choke coil to. Choke coil 60 connects with lead 58 and thus the plate of tube M is supplied with the correct degree of positive potential from the power supply.

The plate circuits of tubes 43 and 44 are connected through the coupling condensers El and 62 to the control elements, i. e., the grids, of the tubes in the phase control unit. Thus coupling condenser Ei is directly connected with the grid 63 of the tube 56, while coupling condenser 62 is directly connected with the control grid 65 of thermionic tube 55.

The grids of tubes 64 and 66 are each connected to special C/L circuits. Thus grid 63 is connected I to the circuit including inductance 5? and variable input from stage it to the control grids of stage l2 with undisturbed phase characteristics. The ci cuit is so designed that the energy from the oscillater stage is fed to the control elements of the modulation stage with unchanged and undistorted phase. With the type of interstage coupling shown, this can in most circumstances be secured by having the constants of the several C /L circuits of the same value.

Like the isolating stage, the phase control stage comprises in effect a dual circuit. The two tubes employed in this circuit are disclosed as of the directly heated cathode type. The tube 64 is provided with a cathode 1| which is connected to the grounding and filtering network comprised by resistor 12 and the condensers l3 and I i. The function of the resistor is to permit the connection of the electrical center of the filament to the common ground. The condensers function to offer a short path to the common ground for the radio frequency energy operating within the circuit and secondly to stop or block this energy from following the cathode Wires to the power supply.

This is to insure the stability in previous portions of the transmitter circuit which operate at a lower level of radio frequency energy.' The cathode and the associated connections of tube 66 are identical with those of tube 64. Thus the cathode i5 is connected to the grounding and filtering network including resistor l6 and condensers 1? and 78.. The heating current for cathodes l4 and "i5 is obtained from the power supply through leads E9 and 80.

It will be noted that the low point of inductance 67, which is bypassed through the tap to the common ground by the bypass condenser M, is additionally filtered by choke coil 82. Similarly that point on inductance 69 is bypassed to ground through condenser 83 and additional filteringis secured through choke coil 8 The low end of coils 82 and 8 3 are connected common to lead 85 and are supplied through this lead, from the power supply, with the correct degree of negative potential.

The tapping arrangement on inductances t? and 69 is an important feature of the present embodiment. This is desirable in order that a source of radio frequency; potential, opposite in the inter-electrode capacities between the control grid and plate of tubes {i l and fit. It will be understood that the necessity for neutralization of the inter-electrode capacity is in a sense inherent in the triode tube.

The plate of tube Mis directly connected with the C/L circuit comprising inductance 88 and' variable capacitance 85!. Similarly the plate of tube 66 is connected with the circuit including the Thus, as shown, circuit Bil-4S9 has a preponderance of inductance and is, therefore, inductive inductance Bil and associated variable capacitance 60 in eifect, that is to say it functions to cause the voltage in that circuit to lead the current. Circuit H 9li9l, on the other hand, contains a prepon-' deranoe of capacity and is capacitative in effect, and hence will cause the voltage to lag the current. It is to be clearly understood that the energy from the oscillator stage If! is fed through the isolating circuit with its phase characteristics unchanged. Assuming this energy fed into the tubes of the control stage I 2 to be of 'the reference or standard voltage phase angle. it will be-seen that the circuits 88-439 and -9} operate conjointly and'r sequentially toshift the voltage phase angle of, the energy to lead and lag positions. two circuits cause the voltage phase angle to shift or reciprocate with respect to the main or medial phase angle established at the oscillator stage.

Circuits 88-89 and Bil-5 are associated or coupled to a radiator which functions to transmit or radiate energy with themodified phase angle. In order to eliminate undesired shifting or. distortion of the phase angle, in the antenna proper,

Thus these i the antenna circuit is designed so as to have a negligible reactance.

At this point it will be appreciated that if devicesare associated with the output circuits of tubes and 66, which modify the phase angle iii't proportionately to the intelligence input energy in the devices, a definite means of modulating the radiated signal in accordance with this input ener y is available. The inductances 3d and of tubes Fi l and 55 respectively are coupled to individual secondary sections 92 and 93. These two inductances or secondary sections are directly connected together. Across the extremities of the circuit thus formed is connected the capacitance S2. The circuit is completed with the radiator or antenna 95. The capacitance is so adjusted as to cause the antenna circuit to resonate at the frequency which is desired to be utilized and which is gen food at oscillator it. This antenna circuit is adjusted to have as low a reactance as is practically possible. In other words the capacity to inductance ratio in this circuit is so ad justed to cause the voltage phase angle to equal coincide with the current phase angle.

In this transmitter when no microphonic currents are utilised the signal emanating from the antenna is a pure radio frequency wave, the voltage phase and current phase angle of which coincide, giving it a unity power factor. All factors of the wave, namely frequency, energy phase angle, wave form and amplitude, remain under this unmodulated condition. however, modulation is imposed the vol e phase angle is made to vary, the angle first leading and then lagging the medial phase angle. It will be noted also that the power factor of the energy likewise varies as it is governed by instantaneous voltage and current phase angle.

When the present structure is used for radio broadcasting, a source of variable or modulated energy is provided. This source may be a microphone as. In lieu of a microphone, of course, any device which is electrically responsive proportionately to variations in the factor to be transmitted may be employed. Th1 s variations in sound, light. temperature, pressure and so forth be made to act upon the element 8% to cause a variable electrical response therein. Energy from the element 96 is fed through an appropriate amplification. stage or stages 9'. and the out it from this stage is connected to the primary 98 of a special transformer. The secondary 9d of the transformer is center tapped at This center tap oi the secondary is connected to the positive end of the standing plate voltage supplied by the power supply. The two ends or extremities of the secondary connect to the plate circuits of the tubes 65 and 66 through the leads H35 and it? respectively. This transformer connection, as shown, is made to the low sides of the plate circuits of the dual phase control tubes. two

tubes, that is to say the two halves of the control circuit, are thus operated under class C operation in which modulation by plate voltage variation secured. In other words, the tubes E i and t6 ar so operated that their output is purely a function of the square of the plate voltage. The low sides of the plate circuits of tubes t t and are by to common ground by condensers 3d and 9 l and additionally filtered by choke coils 3S respectively, thus preventing feed back of radio frequency energy through ml and iitfi. to the microphone circuit.

It will thus be seen that the output of the units of the phase control system, specifically the tubes and 68, independently present a substantially linear variation with the square of the plate voltage. The plate voltage is represented by a standing D. C. voltage with the positive at the plate and the negative at the cathode or filament. In series with this isintroduced an alternating or pulsating voltage, thus increasing or decreasing the effective operating plate voltage. The plate voltage therefore is constant when the system is unmodulated, but varies with modulation.

It will now be appreciated that when the element ilfi is actuated one end of the secondary will have a positive polarity in respect of this center tap and at the same time instant the other end will have a negative polarity. given instant one of the tubes in the control stage ii. will have an increased plate voltage when its section of the secondary 951 has a positive polarity. The output of this tube will, therefore, increase. This increase will be substantially linear following the ratio of the square of the sum of the standing plus the peak voltage established at a given instant between the extremity of the secondary and the center tap to the square of the standing plate The other half of the control circuit at voltage. this same instant is subjected to negative polarity and will have a corresponding decrease in plate voltage. The voltage from either extremity of the special transformer to the center top will be the same at any given instant but will differ only in clarity.

As the amplitude of the output of one half of the control unit, say tube M, is increased by the introduction of positive potential from the transformer, the amplitude of the output of the other half of the circuit, tube 66,.is decreased less absolute amount by the simultaneous introduction of an equal amount of negative potential from the same transformer. Thus, paradoxically, while true amplitude modulation is in fact utilized in each half of the circuit (i. in each tube), the correlation and interaction of the tubes and the difierential reactance circuits is such as to completely nullifyor eliminate the amplitude effects in the final output.

It is thus evident that amplitude variations as such are not utilized in this modification of the invention. It is to be noted, however, that the differentially reactive circuits 8389 and fill-9! are associated with the tubes 54 and 66 respectively. The maximum relative load, passing through tubes 64 and 65, followin the microphonic variations, reciprocates from one-half of the control circuit to the otherand is alternately reacted upon by the positive and negative reactance of the (inferential circuits. There is thus imposed on the output energy a shift or displacement of the voltage phase angle corresponding to the microphonic input, while nevertheless maintaining the frequency of the original or carrier energy at a substantially constant value so far as the modulation factor is concerned.

This will be seen to be true in view of the fact that the carrier energy is impressed on each the grid of tube 64 and tube SS in exactly the same frequency amplitude and phase as this energy is generated in tube 3!. Such energy therefore, up to its introduction on grids 53 and 65, is maintained at a constant value under allconditions. As explained, the microphonic or modulating effect operates upon the output energy from these last tubes, i. e., tubes 5% and it. The differential reactance circuits BEL-B9 and iii -fil then operate upon the energies from tubes 5 3 and 68 so as to modify the voltage inverse current phase angle Hence at any of the transmitter more flexible.

positions, these positions being a function of or controlled by the modulating or microphonic circuit. The energy as thus modulated is then fed immediately and directly to the antenna, without any further interaction in thermionic devices and is thus radiated. It will thus be seen that the voltage inverse current energy and the current inverse voltage energy are mixed directly in the output circuit. There can thus be no change in frequency in the energy radiated from the antenna.

The alternating energy of substantially constant frequency and amplitude but of varying voltage phase angle is transferred to the secondary or antenna circuit, in the manner described. Since this secondary circuit is so designed as to have substantially negligible reactanc e, that is to say negligible effect upon the microphonically displaced phase angle, the carrier wave is radiated as energy of substantially constant frequency and amplitude but with a modulated voltage phase angle.

It will be appreciated that within the scope of the invention there are a wide number of variations permissible. A typical example of one of these is shown in Fig. 2. This illustrates a modification of the secondary or antenna circuit and is designed to subserve a number of functions. In the first place it serves to make the operation Its operation is quite analogous to that of a fly-wheel operating to lock the medial voltage phase angle of the secondary or antenna circuit at the fixed predetermined value. In one form the circuit may comprise a self controlled oscillator M3 provided with the filament grid and plate elements m4, I05 and I86 respectively. The tube may take the form of a directly heated cathode and is shown as of the same type as tube 64 and E6. The cathode may be connected to a grounding and filtering network including the resistor III! and the condensers Hi8 and H39. Heating current is supplied to the filament through the leads HI) which may be suitablyconnected to the power supply. The plate is connected in /1. circuit with the inductance III and variable condenser or condensers H2. The inductance III forms a primary of a variable inductive coupling to the-secondary circuit, the secondary of which is formed by the coil H3. This type of circuit is a self controlled oscillator, the frequencies of the oscillations of which are a function of the resonant frequency of the inductance capacity circuit 'I II-I I2. The frequency control circuit is so designed and/or adjusted as to have the same medial voltage phase angle as the energy fed through the system from the frequency generating stage It. The reference or medial phase angle of this circuit is the same as that of the energy fed to the grids of tubes 64 and 66.

It will be understood that although this circuit is shown as a self controlled oscillating circuit of the so-called TNT variety utilizing an aperiodic grid circuit I95, it may well take the form of any suitable externally controlled oscillator.

It will be appreciated from the description of the apparatus in Fig. 2 that it operates'to fix or stabilize the medial voltage phase angle of the antenna circuit proper. Since the oscillator Hi3 has the inductance Ill and capacitance H2 so adjusted as to establish its C/L ratio in conformity to the C/L ratio of circuit 3 1-35, it will function to establish this exact medial voltage phase angle of the energy in the antenna circuit proper. In a mechanical sense then it tends to pull the medial phase voltage angle of the antenna circuit into step with its own medial voltage phase angle and to lock the former in its desired value.

Since the circuit IHI I2 may be adjusted to any practically desired value, the tube may be operated at a frequency different from the resonant frequency of the secondary or antenna circuit. In such circumstances it will react with the antenna circuit to produce a beat frequency. By reacting on the main energy passing through the transmitter sysem with a signal, and in such circumstances as to shift the voltage phase angle of the frequency in accordance with the signal, a new type of secretsignalling system is thus provided. Such a signal, comprising a variable or shifting voltage phase angle of a heterodyned transmitted wave may bereceived only by a receiving system designed with particular reference to the transmitter and corresponding precisely with it in the major functioning principles. By proper adjustment of the circuit lII-I I2 various other modified reactions on the energy in the antenna circuit may be obtained.

The improved results secured with the structure shown in Fig. 2 may be achieved with other, and specifically different, arrangements, such as shown in Fig. 3. This is illustrated to disclose the utilization of an amplifier type of circuit in lieu of the oscillator type shown in Fig. 2.

The amplifier tube I I5 is shown as of the screen grid, directly heated cathode type. The filament H6 is suitably connected to a source of heating current and like the filament of tube I03 is provided with an efiective grounding and filtering arrangement. The grid H6 is capacitively cou- .pled to the main oscillator circuit Ill and is stabilized by the correct degree of negative potential being introduced through choke coil 44', the low side of which is bypassed to the common ground by condenser 45. The plate I I! is connected to a circuit comprising the inductance H8 and parallel variable condensers H9 and I20. This C/L circuit, like circuit I I I-I I2, in the preferred operation is so chosen as to constants and is so ad justed as to positively establish a medial or reference phase angle in exact conformity with the phase angle of the energy transferred from the oscillator circuit Iii through the coupling condenser 40 to the main control. circuit.

The inductance H8 forms a primary of a variable inductive coupling to the secondary circuit, the secondary of which is formed by the coil I2 I.

The tube H5 is shown as excited directly from the frequency source of the transmitter.

Like the circuit shown in Fig. 2 the circuit of Fig. 3 may be adjusted to produce any desired beat note, a harmonic or submultiple of the frequency of the output energy from circuit III,

It will be understood by those skilled in the art that the fly-wheel circuits of Figs. 2 and 3 may shown in Figs. 2 and 3, is given merely to illustrate the major concept here involved, that is to accomplish modulation by varying the phase characteristics of an energy of constant amplitude and frequency in order to obtain a modulated signal.

Thus in lieu of the method inhering in Fig. 1 the voltage phase angle may be controlled in accordance with modulating currents by varying the capacitance-inductance ratio by varying the capacitance inversely with the inductance, or vice versa, in one circuit, the resonant period remaining the same. Again, the voltage phase angle modulation may be accomplished by varying the voltage phase angle of the resonant frequency of a piezo electric crystal or a magneto-striction element, such as a mass of a particular nickel alloy.

Also this voltage phase modulation may be achieved by microphonically varying the capacity associated with an aperiodic circuit; similarly this same result may be accomplished in this type of circuit by varying the inductance.

Thus the new type of modulation may be effected by varying the voltage phase angle output from a dual circuit composed of two reacting aperiodic circuits, in one of which inductance and in the other of which capacitance predominates. Modulated output may be obtained in this type by first allowing one circuit to represent most of the output, and then alternately allowing the other to represent the major output.

When factors other than the voltage phase angle are utilized as the effective modulating means, it will be understood that the receiver is designed to be actuated by or responsive to one or more of these three variable factors in the transmitted signal.

In the embodiment chosen for illustration the receiving circuit, shown in Fig. 4 is designed to be actuated by variations in the voltage phase angle. But as noted above, such receiver may readily be adapted to be responsive to the other two variable phase characteristics.

In its essentials the receiver comprises means to receive the transmitted signals, means for coupling the signal receiving means to a special demodulator circuit, means to supply a constituent reacting with the received signal, means for isolating the reacting demodulating operation from the output connection, and an element or elements in the output connection which is proportionately responsive to the effective modulating energy input. The receiver is also provided with a power supply for supplying the power requirements of the operative elements of the receiver.

As shown in Fig. 4 the receiver proper comprises the antenna circuit designated generally by the numeral I30, the coupling and demodulating stage I3I, which corresponds in general function to the control stage I 2 of the transmitter, the reacting circuit I32 which serves primarily to balance out or neutralize the received frequencies, thus leaving the stage I33 to be operated by the shifting voltage phase angle, or other phase characteristics chosen and which actuates the signal responsiv element I34.

The receiver is provided with a power supply entirely comparable to the similar unit in the transmitter. This is connected to a source of power which is usually a sixty cycle A. C. current.

The power line is connected to a transformer primary I35. This has such a copper to iron ratio as to elTectively operate on the alternating energy available. The primary is provided with taps I36 so as to adjust varying line voltages. The secondary comprises a number of different sections I38, I34 and I40. The core MI is connected, as shown, to common ground so as to minimize the effects of radio frequency energy flowing from the secondary to the primary and thence to the line and also the energy flowing from. the line to the secondary through the primary.

Secondary I38, which is designed to supply the high voltage, is center tapped at I42. The extremities of this winding each connect to a plate of a half wave rectifier, two of such tubes I43 and I44 being employed to secure full wave rectification. The center tap lead I42 forms the negative pole of the rectifier output.

The secondary section I39 provides the heating current for the filaments of the rectifier tubes. This secondary is likewise center tapped by lead I 45 and the tap forms the positive pole of the rectifier output. The third section I48 provides the heating current for the tubes in the receiver. This is center tapped and grounded, as shown at Like the transmitter power supply, the negative pole of the rectifier system is connected, through lead I42, to the negative end of the voltage dividing resistor 147, the negative end of the filter condensers, the negative end of the stabilizing condenser. The positive pole is connected through lead I45 to the positive end of the first filter condenser, first filter reactor, thence through this reactor to the positive end of the second filter condenser to the second filter reactor, then to the positive end of the third filter condenser, the positive end of the voltage dividing resistor, and finally to the point in the receiver proper requiring the highest positive potential. Since these parts have been fully described in Fig. 1, the numerals are here omitted to simplify the drawings.

Some point near midway on the voltage divider resistor is connected through lead I48 to common ground and to the intermediate filter condensers. It will be observed that points between this ground point of the voltage divider and the positive end may be utilized to obtain varying degrees of positive potential. Similarly points between the ground point of the divider and the negative end may be used to give varying degrees of negative potential. The power supply is thus adapted to fulfill all the power requirements of the system.

The antenna system which receives the transmitted waves may comprise any suitable aerial iEll. This is connected to the inductance coil II and thence to ground. Preferably the leakage resistance between the antenna and the return path should be as high as possible so as to insure efficient operation.

The circuit I3I is a dual circuit. This comprises the thermionic tubes I52 and I53. This circuit is designated as the amplitude filter demodulator circuit since in its operation the transmitted carrier frequency is nullified or eliminated, leaving only the efiective modulation directly in its pure form.

The tubes I52 and l53 are preferably, though not necessarily, of the indirectly heated cathode screen grid type. Tube I52 is provided with a heater 54, a cathode or electron emitting element I55, a grid I56, plate I51 and screen grid I58. Tube I53 may be of identical construction,

having a cathode I68, grid I6I and plate I62.

The grids I56 and I SI are each connected directly to the high end of a CL circuit composed of the inductance I63 and the capacitance I84. The inductance I63 serves as the secondary of the'aerial circuit, being coupled to the primary I5I. The circuit Ifi3-I64 is so designed and/or adjusted as to have a reference or medial voltage phase angle equal to or coinciding with the medial voltage phase angle in the transmitter and to have negligible reactance. The low end of circuit I 83I55 is connected to ground and the high end, as noted, to the grids in the demodulating circuit.

The cathode I55 is connected to common ground through the resistance I65 and is bypassed to ground through the condenser I65. Similarly the cathode I5!) is connected to ground through resistance I6! and bypassed to ground through condenser I68. The function of these resistances is to allow the plate current IR drop to impose the optimum positive change on the cathodes in respect to the common ground. In this manner, since the control grid circuits return to common ground, the grids will have a charge of the correct sign and value, with retionally filtered by choke coil spect to the cathode. The condensers I56 and I68 establish a short path for the alternating signal energy between the common ground and the cathodes.

The screen I58 is bypassed to common ground through the condenser I69. This screen is addi- I'III. Similarly screen III of tube I53 is bypassed to common ground by condenser I I2 and is further filtered by choke H3. The low end of choke coils H0 and I13 have a common connection to lead I'M and through this are connected to the power supply so as to receive the proper degree of positive potential.

The plate circuits of tubes I52 and I53, so to speak, are functional counterparts of the plate circuits of tubes 54 and 66 of the phase control dual circuit. Thus, plate I5? is connected to a circuit including inductance I I5 and variable ca-- pacitance I16. Plate I62, of tube I53, is likewise connected in a circuit including inductance Ill and variable capacitance I18. The plate circuit of tube I52, as will be seen, contains a preponderance of inductance while plate circuit of tube I53 contains a preponderance of capacitance. The two circuits, are designed to present a certain voltage phase angle. In the circuit of predominant inductance, the voltage phase angle will lead that found in the standard or medial voltage phase angle circuits. In the circuit of predominant capacitance, the voltage phase angle will lag that found in the standard C/L circuit.

These two differential reactance circuits are coupled to individual secondaries, inductance II5 of tube I52 being coupled to the secondary coil Eli? and inductance I I! being coupled to secondary coil IBII. The secondaries I19 and I88 are adapted to be connected together and in the circuit thus formed is the capacitance IIlI. The capacity IBI is so adjusted that the circuit will resonate at the frequency of the signal being received. The ratio of inductance to capacity in circuit I I9I8IJI8I is fixed and is so established as to cause the voltage phase angle to equal and coincide with the current phase angle, or in other words to have unity power factor.

Circuits I 'I5I I5 and IIII'I8 are grounded and filtered in the same manner as the corre sponding circuits connected to tubes 55 and 65 of the transmitter.

Associated with the demodulator circuit just described is the generator stage I32. In the preferred embodiment this performs two major functions. First it generates and introduces into the demodulator circuit oscillations of the exact character as those generated at the transmitter and due to the reaction the carrier frequencies, as such, are nullified or eliminated. In the second place, due to its operation, it serves to establish a fixed medial voltage phase angle in the receiver which serves as the point of reference for the shiftable voltage phase angle of the signal as fed to the voltage responsive coupling tube I33.

The generator stage comprises the tube I32 which preferably is of the indirectly heated cathode screen grid type of tube. This has a cathode heater I 95 suitably connected to the filament heating secondary MEI. The cathode ISI is grounded through resistance I92 and is bypassed to'ground through condenser I93. The screen I94 is bypassed to common ground through the condenser I 95 and the low end is connected through the filtering choke coil to lead I I4. Through this .lead the screen is supplied with the correct degree of positive potential.

The purpose of the cathode resistance I92 is to cause the cathode to have an optimum positive charge in respect to the common ground, and in this way, since the control grid connects directly to common ground, the control grid has the correct sign and value of charge in respect to the cathode.

The plate I95 is connected to a flexible C/L circuit comprising the inductance coil I9? and the adjustable condensers I98 and I99. The coil IQ'I is coupled to the variable coupling coil 2% in the output secondary circuit of the demodulator. The low end of circuit IQ'II98 is bypassed tothe common ground through the condenser MI and is additionally filtered by choke coil 202. The low end of the choke is connected to the power supply so as to provide for the correct degree of positive potential.

The variable coupling between the generator stage and the demodulating stage not only allows for the introduction of energy of constant amplitude and frequency but also of adjustable voltage and current phase angle into the low end of the secondary circuit of the demodulator. Also this coupling allows that portion of the signal energy that is in coil of the secondary circuit (under the proper adjustment of condensers I 98 and I99) to pull the frequency of the generator circuit into step or synchronism with the signal frequency. It is to be noted that the inertia of circuit I9'5I98 does not allow the voltage phase angle to vary with that of the incoming signal. Thus the generator circuit becomes a reacting circuit, the reaction being effective between the high end of the secondary circuit Il92l@ and the common ground.

A coupling device which is a voltage operative unit is connected to the high side of the secondary circuit of the demodulator. The coupling tube is provided with an indirectly heated cathode. The heater 255 is connected to the power supply and the cathode 255 is connected to common ground through resistance Bill and is bypassed to ground through condenser 201, the functions of which have already been described. The grid 208 is directly connected to the high side of the secondary circuit IISI8II. Plate 255 connects the output post or terminal are. The other'output terminal ZIZ is connected to the power supply through an isolation filter and line ZIB. The purpose of this isolation filter is to allow the modulation frequencies to remain, in their pure form, free of any disturbances that might be introduced through line M3 from the associated equipment and power supply. Output posts 2m and H2 contain the modulation frequencies in their pure form and may be utilized from then on in any desired manner.

In sound reception, modulation frequency amplifying stage or stages Ell may be employed.

Associated with the output is the responsive device 33 3. This is representative of any type of instrument or apparatus that the modulation frequencies are intended to affect.

The ccaction cf the several units of the receiver will now be appreciated. The reactor circuit is so adjusted that the oscillations generated therein are in synchronism with the signal frequency fed to the demodulation circuit, but

substantially 180 out of phase with the signal frequency. From this the interaction of the reactor stage and the demodulating stage will be appreciated. Since one frequency is reacting with a like frequency, the incoming signal frequency is thus nullified or eliminated and the grid of the final coupling tube lSS is subjected only to static voltage fluctuations corresponding to the voltage phase angle variations.

It will be clear that the only factor that can alter the plate current of the coupling tube is a change in the relation between the voltage phase angles of the local reactor and the incoming signal. Since the voltage phase angle of the local reacting energy is established at a fixed value, it follows that the plate current of tube m3 follows only the variations in the voltage phase angle of the incoming signal. The plate current, therefore, accurately corresponds to the modulating efiects impressed at the transmitter. When these are audio frequency modulating effects and the responsive device LE -l is a loud speaker, or similar audio responsive unit, the musical notes are reproduced in precise faithfulness and full clarity.

It is particularly to be observed that the amplitude filter demodulator is, so to speak, of dual construction. The plates of the two tubes are connected to C/L circuits of differential reactance. It will be seen that each half of this dual circuit will be more responsive to a particular voltage phase angle in the received signal,

ence the voltage phase angle modulated signal cannot aifect the two halves of the circuit to the same extent at the same instant. However, all other characteristics of the received energy, not having this variable component, will be cancelled out since they will afiect each half to the same extent at the same instant. This is so because the secondary circuit is interconnected in such a way that like values of energy introduced at the same instant, from the two halves of the preceding circuit, will oppose each other and hence cancel out. It will be observed that if amplitude modulated signals are introduced into the system they will likewise be nullitied and cancelled because of the special nullifying action of the dual circuit on this particular type of energy. Since static is one form of amplitude modulated energy and since amplitude energy is nullified, this novel receiver is in truth an amplitude filter.

Again, it is known that the reaction between two substantially constant amplitude alternating energies will simultaneously alter the amplitude of each of these two energies. The amplitude modulation thus effected directly follows the heterodyne beat, or difference between the freuencies. I-leterodyne or beats between two or more sources of alternating energy effect a condition of amplitude modulation on each source of energy. Thus heterodyne frequency is energy in an amplitude modulated form. The new circuit, as noted, filters out or nullifies all such amplified modulated energy. 1

To more clearly illustrate this special function of the dual demodulator circuit, it is so designed as to permit the efiects of amplitude modulation to feed through the system. As shown in Fig. 4, in the secondary circuit l'i9l8li of the demodulator is connected the polarity reversing switch 2H5. In the normal or usual operation the inductances ll9 and I89 are connected together in such a manner that like values of energy introduced into the secondary from the two halves of the preceding circuit, at the same instant, will mutually oppose, and since they are equal they will nullify each other. However, by connecting one of the coils H9 or I80 into the secondary circuit in the opposite polarity, it will be seen that such energies will not oppose but will amplify each other. It has actually been demonstrated that a receiver, constructed according to the circuit of Fig. 4, can be made responsive to the usual amplitude modulated signals, by proper operation of switch 216, and that furthermore amplitude modulations from a nearby high power station can completely be eliminated while, nevertheless, phase modulated signals are received in full clarity.

In view of this it will readily be apparent that the improved receiver may be adapted as a dual functioning device, receiving not only special phase modulated signals but also the typical or usual amplitude modulated signals. The duality may likewise be extended to the complete system, that is to say to the transmitter as well as the receiver. Thus within the scope of the invention one source of intelligence may be utilized to efiect the amplitude of the transmitted signal, to secure amplitude modulation, and simultaneously another source of intelligence may be used to effect voltage phase angle modulation. The two sources of intelligence may be isolated in one receiver of the proper design or may be received in two receivers, one of which is responsive to the amplitude modulated signal and the other to the phase modulated signal.

This type of dual operation lends itself very readily to secret signalling. It is understood however that the preferred form of commercial utilization of the phase principle involves the use of the special type of transmitter and receiver described inasmuch as when operating with this novel system the disadvantages of amplitude modulation discussed hereinbefore are eliminated.

The reactance circuits |ll16 and I'l'l|'l8 have been described as of a differential reactance, one of the circuits being inductive in reactance and the other capacitative. These have been described as of fixed or established value, that is to say their constants are unaffected by the modulations in the system for any given operation. It will be readily understood, however, that in the receiver, by the proper utilization of adjusting mechanism, such as gang control systems, these two circuits may be varied in their absolute values so as to tune the receiver to carrier waves of different frequency.

It is to be understood, therefore, that the appended claims are to be limited, in interpretation, only by the prior art and within the comprehensive scope of the invention as defined herein.

I claim:

1. In an apparatus for implanting intelligence on an electrical wave energy of predetermined amplitude and frequency comprising branch circuits connected in parallel to a source of carrier waves, means for amplifying the energy in each branch, means for implanting intelligence difierentially on the amplitude characteristic of the energy in each branch, transformers having a reactive primary connected in each branch, the

reactance in the primary of one transformer being equal in extent and of opposite sign to that of the other, means for coupling the secondaries of the two inversely'reactive transformers to a common series circuit from which the energyis radiated.

2. In a phase modulating apparatus, means for generating an electrical energy wave, branch circuits through which the energy is directed, a

capacitative reactive transformer in one branch and an inductive transformer in the other,

branch, said transformers having their secondaries connected in series, means to cause differential amplitude modulations within the branches 7 in accordance with superimposed intelligence energy and means to radiate the energy from the secondary circuit of the transformer, the transformers being so adjusted that there shall be radiated a wave of substantially constant amplitude with wave variations therein corresponding to the superimposed intelligence. l

Means for impressing phase modulations at signal frequency on carrier frequency oscillations including, a pair of thermionic tubes having their input electrodes energized by said carrier frequency oscillationa'means for varying the impedance of said tubes in phase opposition at signal frequency, and tuned circuits connected with the output electrodes of said tubes for relatively shifting the phase of the oscillations repeated insaid tubes.

MARSHALL LYTTON DULL. 

